Serum proteins reflecting inflammation, injury and repair as biomarkers of disease activity in ANCA-associated vasculitis

Abstract

Objective: To identify circulating proteins that distinguish between active anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) and remission in a manner complementary to markers of systemic inflammation.

Methods: Twenty-eight serum proteins representing diverse aspects of the biology of AAV were measured before and 6 months after treatment in a large clinical trial of AAV. Subjects (n=186) enrolled in the Rituximab in ANCA-Associated Vasculitis (RAVE) trial were studied. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels were available for comparison. The primary outcome was the ability of markers to distinguish severe AAV (Birmingham Vasculitis Activity Score for Wegener's granulomatosis (BVAS/WG)≥3 at screening) from remission (BVAS/WG=0 at month 6), using areas under receiver operating characteristic (ROC) curve (AUC).

Results: All subjects had severe active vasculitis (median BVAS/WG=8) at screening. In the 137 subjects in remission at month 6, 24 of the 28 markers showed significant declines. ROC analysis indicated that levels of CXCL13 (BCA-1), matrix metalloproteinase-3 (MMP-3) and tissue inhibitor of metalloproteinases-1 (TIMP-1) best discriminated active AAV from remission (AUC>0.8) and from healthy controls (AUC>0.9). Correlations among these markers and with ESR or CRP were low.

Conclusions: Many markers are elevated in severe active AAV and decline with treatment, but CXCL13, MMP-3 and TIMP-1 distinguish active AAV from remission better than the other markers studied, including ESR and CRP. These proteins are particularly promising candidates for future studies to address unmet needs in the assessment of patients with AAV.

Keywords: Autoimmune Diseases; Chemokines; Cytokines.

Figure 1

Levels of selected markers in severe active ANCA-associated vasculitis (AAV), AAV in remission, and in healthy controls. Left panels: receiver operating characteristic curves showing the ability of selected markers to distinguish severe active AAV (at screening) from remission at month 6 (blue curves), and severe active AAV from healthy controls (red curves). The diagonal line indicates what would be expected with no discrimination between groups. Erythrocyte sedimentation rate and C-reactive protein were not measured in healthy controls. Right panels: levels in individual patients. All subjects had severe active AAV at screening and were in remission at month 6. The medians and 95th centiles among healthy controls are shown with horizontal solid and dotted lines, respectively. CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; GM-CSF, granulocyte–monocyte colony-stimulating factor; MMP3, matrix metalloproteinase-3; TIMP-1, tissue inhibitor of metalloproteinases-1.

Figure 2

Correlations between marker levels. Spearman correlation coefficients for all pairs of experimental markers as well as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are shown. Background colour indicates strength of association (red, >0.75; orange, 0.5–0.75; yellow, 0.25–0.5; white, <0.25). BCA-1, CXCL13; FGFb, basic fibroblast growth factor; G-CSF, granulocyte colony-stimulating factor; GM-CSF, granulocyte–monocyte colony-stimulating factor; ICAM-1, intercellular adhesion molecule-1; IFN, interferon; IL, interleukin; IL-8, CXCL8; IL-18BP, interleukin 18 binding protein; IP-10, CXCL10; KIM-1, kidney injury molecule-1; MMP-3, matrix metalloproteinase-3; NGAL, neutrophil gelatinase-associated lipocalin; NGFβ, nerve growth factor β; PAI-1, plasminogen activator inhibitor-1; PDGF-AB, platelet-derived growth factor, A and B subunits; RANTES, CCL5; sIL-2R, soluble IL 2 receptor; sIL-6R, soluble IL 6 receptor; sTNF-RII, soluble TNF receptor II; TARC, CCL17; TIMP-1, tissue inhibitor of metalloproteinases-1; VCAM-1, vascular cell adhesion molecule-1.